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91.
Beatrice Meini 《Numerische Mathematik》1997,78(1):39-58
Summary. By performing an accurate analysis of the convergence, we give a complete theoretical explanation of the experimental behaviour
of functional iteration techniques for the computation of the minimal nonnegative solution of the matrix equation , arising in the numerical solution of M/G/1 type Markov chains (here the 's are nonnegative matrices such that the matrix is column stochastic). Moreover, we introduce a general class of functional iteration methods, which includes the standard
methods, and we give an optimality convergence result in this class.
Received September 1, 1995 / Revised version received September 9, 1996 相似文献
92.
Tsutomu Nakada Ingrid L. Kwee Beatrice V. Griffey Richard H. Griffey 《Magnetic resonance imaging》1988,6(6):633-635
Images of the rat head reflecting glucose utilization were obtained using 2-fluoro-2-deoxy-D-glucose (2-FDG) and 19F nuclear magnetic resonance (NMR) imaging. Spatial heterogeneity of glucose utilization in the rat head was clearly demonstrated showing significantly higher glucose utilization in the brain as compared to the surrounding tissues. Although the potential adverse effects of the high doses of 2-FDG (400 mg/kg) needed to perform the study preclude immediate application of this technique to clinical quantitative glucose utilization studies, the present study shows potential for future development of glucose utilization imaging by NMR. 相似文献
93.
Raffaele D’Ambrosio Martina Moccaldi Beatrice Paternoster Federico Rossi 《Journal of mathematical chemistry》2018,56(10):2876-2897
Adapted numerical schemes for the integration of differential equations generating periodic wavefronts have reported benefits in terms of accuracy and stability. This work is focused on differential equations modelling chemical phenomena which are characterized by an oscillatory dynamics. The adaptation is carried out through the exponential fitting technique, which is specially suitable to follow the apriori known qualitative behavior of the solution. In particular, we have merged this strategy with the information coming from existing theoretical studies and especially the observation of time series. Numerical tests will be provided to show the effectiveness of this problem-oriented approach. 相似文献
94.
A Biomimetic Nickel Complex with a Reduced CO2 Ligand Generated by Formate Deprotonation and Its Behaviour towards CO2
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Philipp Zimmermann Santina Hoof Dr. Beatrice Braun‐Cula Dr. Christian Herwig Prof. Dr. Christian Limberg 《Angewandte Chemie (International ed. in English)》2018,57(24):7230-7233
Reduced CO2 species are key intermediates in a variety of natural and synthetic processes. In the majority of systems, however, they elude isolation or characterisation owing to high reactivity or limited accessibility (heterogeneous systems), and their formulations thus often remain uncertain or are based on calculations only. We herein report on a Ni?CO22? complex that is unique in many ways. While its structural and electronic features help understand the CO2‐bound state in Ni,Fe carbon monoxide dehydrogenases, its reactivity sheds light on how CO2 can be converted into CO/CO32? by nickel complexes. In addition, the complex was generated by a rare example of formate β‐deprotonation, a mechanistic step relevant to the nickel‐catalysed conversion of HxCOyz? at electrodes and formate oxidation in formate dehydrogenases. 相似文献
95.
F. Mayolet P. Reimers Ch. Engelmann 《Journal of Radioanalytical and Nuclear Chemistry》1972,12(2):115-128
The carbon and nitrogen activation curves were determined for the nuclear reactions12C(α, n)15O and14N(d, n)15O, within the limits of the following maximum energies: 40 MeV for α-particles, and 21 MeV for deuterons. Inferences are made concerning the potential possibilities of these activation methods, from the sensitivity aspects, for the determination of carbon and nitrogen, with reference to the problem of the main interferences which have also been studied experimentally. The chemical separation process used to isolate15O after irradiation is described. Concrete examples of carbon and nitrogen determinations by these methods are given. 相似文献
96.
In order to determine the specific effects of radical-induced reactions in the absence of complicating excited-state pathways, four different thiohydroxamic esters and their parent molecule, N-hydroxypyridine-2(1H)-thione, have been studied in murine L1210 leukemia cells for their ability to produce photobiological damage. Irradiation (Xexc= 355 nm) of cells in the presence of thiopyridone esters, specific photolytic precursors of sulfur-, carbon- and oxygen-centered radicals, caused toxicity that was unambiguously demonstrated to result from radical photosensitization mechanisms. Cellular morphological changes were observed following irradiation but apoptosis was not found to take place. A good correlation was evident between lipid peroxidation, measured by the thiobarbituric acid method, and phototoxicity, assessed by the trypan blue exclusion assay, indicating that the ester derivatives exert their effects mainly in plasma and/ or subcellular membranes. Irradiation performed under deaerated conditions also induced significant phototoxicity but the effects of deaeration were dependent on the ester used and are discussed in terms of the nature of the primary radical species generated in each case. Irradiation of L1210 cells in the presence of N-hydroxypyridine-2(1H)-thione, a nonspecific, photochemical source of hydroxyl radical, was also found to trigger phototoxicity and lipid peroxidation. However in this case, photodamage cannot yet be definitely attributed to a radical or type II mechanism although the apparent oxygen independence of phototoxicity would indicate that type II contribution is not significant. 相似文献
97.
A divalent europium chloride-bromide phase, EuBr1.56(7)Cl0.46(2) has been prepared and identified on the basis of analytical, X-ray powder diffraction and single-crystal data. Although the phase is considered isostructural with EuCl2 (PbCl2 structure type, a = 0.9230 (5), b = 0.7890 (4), c = 0.4613 (3) nm, space group Pbnm), the single-crystal data indicate long-range order in the form of a superstructure which doubles the b parameter. In the pseudocell the square pyramidal anion sites are occupied principally by bromide ions, the tetrahedral sites almost equally by bromide and chlorine ions. Structural details and the long-range order are discussed. Evidence is presented for the existence of another europium(II) mixed halide phase, EuBr1.8(2)Cl0.16(2). 相似文献
98.
99.
Beck B Larbig G Mejat B Magnin-Lachaux M Picard A Herdtweck E Dömling A 《Organic letters》2003,5(7):1047-1050
[reaction: see text] A general strategy toward macrocyclic compounds using multicomponent reaction (MCR) chemistry, e.g., Passerini and Ugi variants, and ring-closing metathesis (RCM) is introduced. The corresponding bifunctional isocyanides carboxylic acids bearing a terminal olefin are easy to prepare from the corresponding commercially available starting materials. Advantageously, this strategy allows fast access to a diverse conformational space of natural product-like macrocycles and could thus be of interest in the discovery of novel bioactive agents. 相似文献
100.
Ch Engelmann G. Filippi J. Gosset F. Moreau 《Journal of Radioanalytical and Nuclear Chemistry》1977,37(2):559-570
The photonuclear reactions used for this isotopic analysis are as follows:16O(γ, n)15O threshold energy 15.7 MeV;18O(γ, p)17N threshold energy 16.3 MeV.15O is a pure β+ emitter of half-life 2.03 minutes, whereas17N presents a 4.2 second neutron emission. The principle of the method is founded on the simultaneous measurement of the above
characteristic radioactivities, the intensities of which are proportional to the respective quantities of16O and18O present in the irradiated sample. The potentialities of this new oxygen isotope analysis method, based on the use of an
electron accelerator, are described. Detection limit of 0.1 μg18O is easily attainable. The equipment designed and built to industrialise this technique is described. It allows a hundred
samples to be analysed automatically, the accelerator, detection instruments and pneumatic transfer circuits being controlled
by a logic system linked to an electronic chronometer. 相似文献